popa3d is a tiny POP3 daemon. Goals are, in order:

1. Security (to the extent that is possible with POP3 at all, of course).
2. Reliability (again, as limited by the mailbox format and the protocol).
3. RFC compliance (slightly relaxed to work with real-world POP3 clients).
4. Performance (limited by the more important goals, above).

popa3d can be run from inetd, or as a stand-alone server.
Note that it does not itself provide SSL support, but may be wrapped
with relayd or stunnel.

popa3d only uses flock(2) for locking and may not be safe on NFS
or with mail systems that only use lock files.
